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MÖSSBAUER STUDY OF 57Co IMPLANTED IN SILICON AND GERMANIUM
G. Langouche, I. Dezsi, J. de Bruyn, M. van Rossum, R. Coussement
To cite this version:
G. Langouche, I. Dezsi, J. de Bruyn, M. van Rossum, R. Coussement. MÖSSBAUER STUDY OF
57Co IMPLANTED IN SILICON AND GERMANIUM. Journal de Physique Colloques, 1979, 40 (C2),
pp.C2-547-C2-548. �10.1051/jphyscol:19792189�. �jpa-00218566�
JOURNAL DE PHYSIQUE Colloque C2, suppl&ment au n o 3 , Tome 40, mars 1979, page C2-547
G. ~ a n ~ o u c h e * , I . D e z s i If
,
J . De b r u y n , M. Van Rossum and R. CoussementI n s t i t u t voor Kern- en S t r a l i n g s f y s i k a , University of Leuven,
Physics Department, 3030 Leuoen, BeZ g i m
Rdsum6.- Des e x p d r i e n c e s dans d e s g r a n d s champs e x t e r n e s montrent que l e d o u b l e t observd d a n s l e s s p e c t r e s Mgssbauer du 5 7 ~ e d a n s S i e t Ge, p r o d u i t p a r i m p l a n t a t i o n d ' i o n s 1 une dose d e 10"' ou p l u s , e s t dO ii l ' i n t e r a c t i o n q u a d r u p o l a i r e . Dans l e s d o s e s d ' i m p l a n t a t i o n p l u s f a i b l e s on remarque une n e t t e ddpendance de c e t t e d o s e . Des e f f e t s prononc6s d ' a n n i h i l a t i o n t h e r m i q u e s e r o n t d i s c u t i 5 s . A b s t r a c t . - Experiments i n l a r g e e x t e r n a l f i e l d s show t h a t t h e d o u b l e t o b s e r v e d i n t h e Mzssbauer s p e c t r a of 5 7 ~ e i n S i and & , ' o b t a i n e d by i o n i m p l a n t a t i o n t o a d o s e of 10" o r h i g h e r i s due t o q u a d r u p o l e i n t e r a c t i o n . At l o w e r i m p l a n t a t i o n d o s e s a remarkable d o s e dependence was o b s e r v e d . Some pronounced t h e r m a l a n n e a l i n g e f f e c t s w i l l a l s o b e d i s c u s s e d .
I . I n t r o d u c t i o n . - The Mijssbauer s p e c t r u m of implan- t e d 5 7 ~ o and 57Fe i n S i and Ge h a s b e e n i n v e s t i g a - t e d s i n c e l o n g 11-31. C o n f l i c t i n g t h e o r i e s have b e e n used t o a c c o u n t f o r t h e o b s e r v e d s p e c t r a . One o f t h e main p o i n t s o f d i s c u s s i o n i s t h e o r i g i n o f t h e d o u b l e t o b s e r v e d i n t h e Mgssbauer s p e c t r a of 5 7 ~ e i n S i ( f i g u r e 1) and Ge. While some a u t h o r s f a v o r t h e two s i n g l e l i n e s h y p o t h e s i s 11-21, o t h e r s t e n d t o b e l i e v e t h i s i s a q u a d r u p o l e d o u b l e t 131.
F i g . 1 : ~ z s s b a u e r s p e c t r u m of 5 7 ~ o i m p l a n t e d i n S i t o a dose of 10" atoms/cm2.
P a r t of t h i s s t u d y i s d e v o t e d t o an e x p e r i m e n t t o s o l v e t h i s c o n t r o v e r s y . During t h e s e e x p e r i m e n t s a r e m a r k a b l e d o s e dependence was o b s e r v e d , and v e r y pronounced a n n e a l i n g e f f e c t s were found t o b e p r e - s e n t . T h e r e f o r e a more e x t e n s i v e s t u d y o n t h e s e phenomena was u n d e r t a k e n . A d e t a i l e d a c c o u n t o f
' ~ a n ~ e s t e l d Navorser N.F.W.O.
=On l e a v e from t h e C e n t r a l R e s e a r c h I n s t i t u t e f o r P h y s i c s , Budapest, Hungary.
t h e s e e x p e r i m e n t s w i l l be g i v e n e l s e w h e r e , b u t a b r i e f s u r v e y o f t h e o b s e r v e d e f f e c t s w i l l be g i v e n a t t h e end of t h i s p a p e r .
2. E x p e r i m e n t a l . - S o u r c e s were p r e p a r e d by i o n i m p l a n t a t i o n a t room t e m p e r a t u r e of 5 7 ~ o i n t o S i and Ge s i n g l e c r y s t a l s w i t h a n e n e r g y of 70 keV and a d o s e r a n g i n g from 1012 t o 10" atoms/cm2. A n e n r i - ched p o t a s s i u m f e r r o c y a n i d e a b s o r b e r of 0.5 mg/cm2 5 7 ~ e was used. The t h e r m a l a n n e a l i n g o f some sam- p l e s was performed under a f l o w i n g a r g o n atmosphere always f o r a p e r i o d o f t h r e e h o u r s .
3. Measurements i n e x t e r n a l f i e l d . - F i g u r e 1 shows t h e s p e c t r u m o f a s o u r c e o f 5 7 ~ o i n S i , w i t h a n i m p l a n t a t i o n d o s e of 10" atoms/cm2. T h i s i s a n a l m o s t s y m n e t r i c d o u b l e t w i t h l i n e s a t -0.78(3) 4 s and + 0 . 2 1 ( 3 ) mm/s. The a p p l i c a t i o n of an e x t e r n a l f i e l d t o t h i s s o u r c e s h o u l d change t h e s p e c t r u m i n s u c h a way t h a t c l e a r l y c a n be d i s t i n g u i s h e d w h e t t e r t h e s e a r e two s i n g l e l i n e s o r a q u a d r u p o l e d o u b l e t . Measurements were performed i n a n e x t e r n a l f i e l d of 8 0 kG a p p l i e d t o t h i s s o u r c e , and t o a s i m i l a r sour- c e o f S 7 c o i n & , a s we d e s c r i b e d i n d e t a i l i n a r e c e n t p a p e r
141.
The b e s t f i t t o t h e s p e c t r u m i n a n e x t e r n a l f i e l d was c l e a r l y o b t a i n e d w i t h t h e q u a d r u p o l e i n t e r a c t i o n h y p o t h e s i s , a s a a n be s e e n i n f i g u r e 2 f o r t h e c a s e o f S i . The dashed l i n e i n t h i s f i g u r e i s a t h e o r e t i c a l c a l c u l a t i o n c o n s i d e r i n g t h e s e l i n e s a s two s i n g l e l i n e s , b o t h s p l i t by t h e e x t e r n a l f i e l d , w h i l e t h e f u l l l i n e i s a f i t w i t h a combined m a g n e t i c p l u s q u a d r u p o l e i n t e r a c t i o n con- s i d e r i n g t h e two l i n e s a s t h e members o f a quadru- p o l e d o u b l e t .I n d e p e n d e n t l y a s i m i l a r c o n c l u s i o n was r e a c h e d by Sawicka e t a l . / 5 / f o r t h e s p e c t r u m of s t a b l e "Fe,
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792189
C2-548 JOURNAL DE PHYSIQUE
implanted in Si to a much higher dose of 1016 atoms/ for this drastic change in the spectrum has probably
I
I l I I l I Il
- L -3 -2 -1 0 1 2 3
VELOCITY (mm Is1 Fig. 2 : Mcssbauer spectrum obtained by applying 8 0 kG to the source used in figure 1. The gamma rays are detected parallel to the field direction.
4 . Dose Dependence.- During our experiments we dis-
covered that when a lower implantation dose is used the spectrum shape changes drastically. This is illustrated in figure 3 for sources of 5 7 ~ o in Ge with implantation doses of 1012, 1013 and 10"
atoms/cm2 respectively. A similar behaviour was observed for sources implanted into Si. In addition to the quadrupole doublet a substantial single line fraction is present in the Msssbauer spectrum.
to be found in the fact that at these lower doses we are below the amorphisation limit of the crystal.
The quadrupole doublet then reflects those CO atoms that are imbedded in an amorphous surrounding. At lower doses, however, a substantial fraction of the implanted atoms have a chance to land in an undama- ged region of the crystal, and come to rest in a highly symmetric lattice site, giving rise to the single line in the M%sbauer spectrum.
5. Annealing behaviour.- The annealing behaviour of
"CO sources in Si and Ge turned out to be very complex. Especially in Si, every new M'6ssbauer spec- trum taken after a new annealing step IOOOC higher than the previous one turned out to be different. A detailed account of the different observed annealing steps will be given elsewhere. Some major observa- tions were :
-
a recrystallisation of the amorphous layer is clearly observed around 200°C and 300'~ for Ge and Si respectively. This is seen by a sudden collapse of the quadrupole doublet to less than half of its value.
-
at higher annealing temperatures, the behaviour of 5 7 ~ o in Si and Ge is different.-
in the Ge lattice, the CO atoms remain stabilized in a lattice site characterized by a quadrupole interaction, until they start to diffuse out of the lattice.-
in Si, on the other hand, the spectrum is finally dominated by a single line with the same isomer shift as the one appearing in the lower dose unan- nealed spectra, so that in Si the CO atoms seem to stabilize in a more symmetric lattice site than in Ge.This work has been supported by the IIKW (Interuni- versitair Instituutvoor Kernwetenschappen). The au- thors are indebted to Dr. H.Pattyn and to Mr. R.
Vanautgaerden for the careful 5 7 ~ o implantations.
Referehces
/I/ Weyer,G., Grebe,G., Kettschau,A. Deutsch,B.I., Nylandsted Larsen,A. and Holck,O., J.Physique 37 (1976) C6-893.
-
VELOCITY (rnrn/s) /2/ Latshaw-G., Ph.D.Thesis, Stanford University (1971)-
3 : Mijssbauer spectrum of 5 7 ~ o implanted in /3/ Sawi$ka,B.D., Sawicki,J.A. and Stanek,J., J with several implantation doses. Physlque
2
(1976) C6-879./ 4 / Langouche,G., Dezsi,I., Van Rossum,M., De bruyn
Such a behaviour is fairly unexpected as it has J. and Coussement,R., to be published in Phys.
Stat. Sol.
been shown by Sawicka et al. /3/ that at doses ran-
/5/ Sawicka,B.D. and Sawicki,J.A., Phys. Lett.
*
ging from 5 X 10" atoms/cm2to 5 X 1016 atoms/cm2 (1977) 311.
the spectrum remains a symmetric doublet. The reason
